Oxidative hair dye colorants are essential elements in hair dyeing preparations for the permanent dyeing of human hair. The hair dyeing process is achieved, in general, by the reaction of certain dye compounds (known as primary intermediates or primary dye intermediates) with certain coupling compounds in the presence of a suitable oxidizing agent or compound, such as hydrogen peroxide. Oxidative dyes are especially useful for their intense color formation and fastness to light and washing.
In order for procedures using permanent oxidative dyes to work properly, a number of parameters and conditions are important to consider in the use of these dyes in admixture with couplers in hair color preparations for human hair. Among these are the final color and color intensity that are produced after application to the subject's hair; the wash fastness and the light fastness of the resulting dye; the resistance of the dye to perspiration; the type of hair being dyed, e.g., virgin hair or waved hair; and the resistance of the dye to various hair treatments, such as permanent wave, straightening, shampooing, conditioning and rubbing. In addition, the dye must have virtually no allergenicity or dermal adverse reactions. Ideally, the dye product remains stable against the above-mentioned external influences and against chemical agents for a suitable period of time after application to the hair, for example, for at least four to six weeks. The dye-containing composition is economical to produce and has a reasonable shelf life. Further, the components of oxidative hair dye compositions should optimally produce the strongest possible color shades that correspond as closely as possible to the natural hair color nuances.
U.S. Pat. Nos. 4,371,370 and 4,314,809 to D. Rose et al. describe bis(2,4-diaminophenoxy) alkanols and bis(2,4-diaminophenoxy) alkanes, respectively, as coupling compounds in oxidative hair dyes. U.S. Pat. No. 5,114,429 to A. Junino et al. describes compounds consisting of N,N'-bis(.beta.-hydroxyethyl)-N,N'-bis(4'-aminophenyl)-1,3-diamino-2-propa nol and N,N'-bis(ethyl)-N,N'-bis(4'-amino-3'-methylphenyl)ethylenediamine for use in the dyeing of keratinous fibers, including human hair. German Patent Application No. DE 2,934,329 to Henkel describes binuclear analogs of 2,4-diaminoanisole for use as hair dyeing compounds. German Patent Application No. DE 3,235,615 describes bis(2,4-diaminophenyl) alkanes as couplers in hair dye compositions. In general, the primary intermediates and couplers described in these patents and published patent applications are linked by alkyl chains. Phenylalkyl-substituted primary intermediates and couplers are also described in the art. The types of primary intermediates and couplers disclosed in the art are benzene, pyridine and pyrimidine, pyrazolone, naphthalene, indole, indolinone or other heterocyclic rings containing electron-donating groups such as amino, alkylamine, hydroxyl, and alkoxy groups.
A continued need in the art is the discovery of hair dye components, including primary intermediates and couplers, that optimally satisfy all of the above-mentioned requirements and afford advantageous properties to the user. Until the compounds of the present invention, oxidative hair colorants having a phenyl group as a linker were not known or available to those having skill in the art. The structural features of the novel coupling compounds in accordance with the present invention provide two coupler units connected by a phenyl group as a linker, thereby producing coupling compounds that are larger than standard or commonly known human hair colorants and which provide intense and lasting coloration to hair. Indeed, that the compounds of the present invention are able to penetrate hair fibers to produce lasting colors of deep intensity in spite of their large molecular size is a surprising result to those having skill in the art.